What's good for the world isn't the same as what's good for Facebook, CEO Mark Zuckerberg wrote in a leaked email.

The British Parliament released a trove of confidential internal emails from the social networking giant on Wednesday.

The documents provide an unprecedented window into Facebook's ruthless approach to growth.

Facebook CEO Mark Zuckerberg once privately made a stark admission: What's good for the world isn't necessarily what's good for Facebook.

On Wednesday, the UK Parliament released a trove of confidential internal Facebook emails it seized from an app developer who had obtained them as part of a legal battle with the Silicon Valley tech giant. It was an extraordinary move, with the documents supposed to remain under seal by order of a California judge. The publication of the documents has provided an unprecedented window into the inner workings of Facebook's executive team and their ruthless approach to competition.

In one email, sent by Zuckerberg on November 19, 2012, the chief executive candidly discussed his attitude toward providing third-party apps with access to its platform.

"Sometimes the best way to enable people to share something is to have a developer build a special purpose app or network for that type of content and to make that app social by having Facebook plug into it," he wrote.

But, he added: "However, that may be good for the world but it's not good for us unless people also share back to Facebook and that content increases the value of our network. So ultimately, I think the purpose of platform - even the read side is to increase sharing back into Facebook."

In other words: Zuckerberg said that sometimes the best option for people who want to share stuff is to do it via specialized apps, only using Facebook tools to make doing so more social. But that doesn't align with Facebook's interests and aggressive strategy of growth - so the company would instead push to bring this sharing inside Facebook's walled garden, even if it's to the detriment of users and the "world."

It's a far cry from Facebook's outward-facing messaging that it is hoping to make the world "more open and connected."

It also contrasts with a memo top Facebook exec Andrew "Boz" Bosworth wrote in 2016 to his colleagues, in which he defended Facebook's growth and connecting people at any cost, even if people died.

"The ugly truth is that we believe in connecting people so deeply that anything that allows us to connect more people more often is *de facto* good. It is perhaps the only area where the metrics do tell the true story as far as we are concerned," Boz wrote. "That isn't something we are doing for ourselves. Or for our stock price (ha!). It is literally just what we do. We connect people. Period."

The attitude Zuckerberg expressed in the 2012 email was also not unique to him. In an email, COO Sheryl Sandberg agreed with him: "I like full reciprocity and this is the heart of why."

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Here's the email exchange shared in the documents:

MZ email 19 November 2012

'After thinking about platform business for a long time, I wanted to send out a note explaining where I'm leaning on this. This isn't final and we'll have a chance to discuss this in person before we decide this for sure, but since this is complex, I wanted to write out my thoughts. This is long, but hopefully helpful.

'The quick summary is that I think we should go with full reciprocity and access to app friends for no charge. Full reciprocity means that apps are required to give any user who connects to FB a prominent option to share all of their social content within that service back (ie all content that is visible to more than a few people, but excluding 1:1 or small group messages) back to Facebook. In addition to this, in the future, I also think we should develop a premium service for things like instant personalization and coefficient, but that can be separate from this next release of platform...

'We're trying to enable people to share everything they want, and to do it on Facebook. Sometimes the best way to enable people to share something is to have a developer build a special purpose app or network for that type of content and to make that app social by having Facebook plug into it. However, that may be good for the world but it's not good for us unless people also share back to Facebook and that content increases the value of our network. So ultimately, I think the purpose of platform - even the read side is to increase sharing back into Facebook.'

...'It seems like we need some way to fast app switch to the FB app to show a dialog on our side that lets you select which of your friends you want to invite to an app. We need to make sure this experience actually is possible to build and make as good as we want, especially on iOS where we're more constrained. We also need to figure out how we're going to charge for it. I want to make sure this is explicitly tied to pulling non-app friends out of friends.get.' (friends information)

...'What I'm assuming we'll do here is have a few basic thresholds of API usage and once you pass a threshold you either need to pay us some fixed amount to get to the next threshold or you get rate limited at the lower threshold.'